Vapor deposition apparatus

ABSTRACT

Multi-layer coating apparatus and system for coating a substrate having a coating chamber and means for advancing the substrate in a horizontal position through the coating chamber. The coating chamber is provided with means for depositing the coating on the bottom side of the substrate as it is advanced through the chamber. Means is provided for preventing one substrate from bumping into another and for providing a predetermined spacing from the substrates as they are advanced through the coating chamber.

This is a continuation of application Ser. No. 311,783 filed Dec. 4,1972, now abandoned.

BACKGROUND OF THE INVENTION

In the June 1969 issue of Research/Development, there is an articleappearing on page 42 entitled "The L-O-F Semicontinuous ThermalEvaporation Plant" in which there is described apparatus for depositingas many as three layers on the sheet of glass with the sheet of glass ina generally vertical position. This apparatus has a number ofdisadvantages such as the difficulty of providing suitable evaporationsources for evaporating onto vertical surfaces. In addition, suchapparatus has lacked the desired versatility. There is, therefore, aneed for a new and improved apparatus and method which can be utilizedfor coating large substrates.

SUMMARY OF THE INVENTION AND OBJECTS

The multi-layer coating apparatus is utilized for coating substratescarried by a frame. Means is provided which forms a coating chamber.Means is also provided which forms an entrance chamber and an exitchamber. Valve means is provided at the entrance and exit of each of theentrance and exit chambers. Conveyor means is provided for advancing theframes carrying the substrates with the substrates in a horizontalposition through the entrance chamber, the coating chamber, the coatingchamber and the exit chamber. Conveyor spacing means is provided formoving the frames rapidly into and out of the entrance and exit chambersand for preventing the frames from bumping into each other and formaintaining a predetermined spacing between the frames as they travel inthe coating chamber.

In general, it is an object of the present invention to provide amulti-layer coating apparatus which can be utilized for applyingmultiple coatings economically and expeditiously to large substrates.

Another object of the invention is to provide an apparatus and system ofthe above character which can be substantially automatic.

Another object of the invention is to provide an apparatus and system ofthe above character in which precision control is maintained throughout.

Another object of the invention is to provide an apparatus and system ofthe above character in which heating of substrates takes place prior tothe glow discharge cleaning.

Another object of the invention is to provide an apparatus and system ofthe above character in which the substrates, for example glass, aremoved rapidly into and out of the entrance chamber and rapidly into andout of the exit chamber.

Another object of the invention is to provide an apparatus and system ofthe above character in which spacing means is provided for preventingthe substrates from bumping into each other in the apparatus and formaintaining predetermined spacing between the substrates as they travelthrough the apparatus.

Another object of the invention is to provide an apparatus and system ofthe above character in which means is provided for maintaining pressuredifferentials between various chambers.

Another object of the invention is to provide an apparatus and system ofthe above character in which it is possible to maintain the substrateheated to a predetermined temperature in the various chambers and toapply coatings in the coating chamber at various desired temperatures.

Another object of the invention is to provide an apparatus and system ofthe above character in which the glass substrates travel in a horizontalposition.

Another object of the invention is to provide an apparatus and system ofthe above character in which only the frames with the substrates carriedthereby are advanced through the apparatus to make possible the use ofsmall separation valves.

Another object of the invention is to provide an apparatus and system ofthe above character in which simplified conveyor systems are utilizedwhich need only be driven from one position.

Another object of the invention is to provide an apparatus and system ofthe above character which makes it possible to utilize a combinationheating and sealing duct means between the chambers.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment is set forth indetail in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a top plan view of a multi-layer coating apparatus and systemincorporating the present invention.

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1.

FIG. 3 is an enlarged detail view of the section of the apparatusbounded by the line 3--3 of FIG. 2 and particularly shows chamber A ofthe apparatus.

FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 4.

FIG. 6 is an enlarged detail view of the section of the apparatus shownin FIG. 2 bounded by the line 6--6 and particularly shows chamber C.

FIG. 7 is an enlarged detail view of the section of the apparatus shownin FIG. 2 bounded by the line 7--7 and particularly shows a portion ofthe chamber D.

FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG. 7.

FIG. 9 is a cross-sectional view taken along the line 9--9 of FIG. 7.

FIG. 10 is an enlarged detailed view of the section of the apparatusshown in FIG. 2 bounded by the line 10--10 and particularly showing thechamber E.

FIG. 11 is a cross-sectional view taken along the line 11--11 of FIG.10.

FIG. 12 is an enlarged detail view of the section of the apparatus shownin FIG. 2 bounded by the line 12--12 and particularly shows chamber Fand a portion of chamber G.

FIG. 13 is a cross-sectional view taken along the line 13--13 of FIG.12.

FIG. 14 is a cross-sectional view taken along the line 14--14 of FIG.12.

FIG. 15 is a top plan view of the portion of the apparatus shown in FIG.14 with portions broken away.

FIG. 16 is a cross-sectional view taken along the line 16--16 of FIG.14.

FIG. 17 is an isometric view of the conveyor spacer mechanism which isutilized in the apparatus and system.

FIG. 18 is an enlarged detail view of one of the masking assemblies inthe apparatus.

FIG. 19 is a top plan view of the masking assembly looking along theline 19--19 of FIG. 18.

FIG. 20 is a schematic circuit diagram showing the electronics utilizedfor operation of the conveyor advancing assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A multi-layer coating apparatus and system which is shown in FIGS. 1 and2 is particularly adapted for semicontinuous operation and for placingmultiple layers on relatively large substrates of a suitable type suchas large sheets of glass. The apparatus comprises a washer (not shown)which is utilized for washing the substrates which are to be coated sothat they are absolutely clean before they are introduced into anentrance chamber A. The washer delivers the substrates, for example inthe form of sheet glass to a loading elevator where it is mated with aframe and delivered to the loading conveyor 27. The loading conveyor 27is adapted to deliver the substrates one by one to a very large coater28. The coater 28 consists of a large fabricated framework 29 upon whichthere has been mounted a plurality of box-shaped enclosures 31-41. Ascan be seen, particularly from FIG. 2, enclosure 31 encloses chamber A,enclosure 32 encloses chamber B and so forth so that the enclosures 31through 41 enclose chambers A through K, respectively.

A plurality of vacuum pumps of various types are associated with each ofthe enclosures so that each of the enclosures can be evacuated to thedesired degree of vacuum as hereinafter described. Such vacuum pumpingsystems are conventional and have not been shown for all of theenclosures.

A large gate valve V1 is mounted at the entrance of the enclosure 31 andsimilarly a large gate valve V2 is mounted at the exit of the enclosure31. It will be noted that the enclosure 31 has a height dimension whichis substantially less than that of the other chambers. This is becausethe chamber 31 has been made as small as possible because the chamber Ais vented to the atmosphere each time a new substrate is introduced intothe chamber. For this reason it is desirable to keep the chamber assmall as possible so as to reduce the time required to pump the chamberdown to the desired vacuum.

A conveyor assembly 46 is mounted within the chamber A and consists of apair of drive wheels 47 and 48 (FIGS. 3 to 5) which are rotatablymounted in the enclosure 31 on opposite sides of the same. The drivemeans for driving the drive wheels 47 and 48 consists of a dc motor 49mounted exterior of the enclosure 31. The motor 49 drives a gearreduction unit 51 which is mounted upon the framework 29. The outputshaft 52 of the gear reduction unit drives a slip clutch 53. The slipclutch 53 is connected to a shaft 54 which extends through a vacuum feedthrough 56 into the chamber A. The shaft 54 is connected to abellows-type universal joint coupling 57. The coupling 57 drives thedrive wheel 47. The drive wheel 47 is also connected to a universal-typecoupling 58 which is connected to a shaft 59. The shaft 59 is connectedto another bellows-type universal joint coupling 61 which is connectedto the other drive wheel 48. These bellows-type couplings permitexpansion and contraction of the shaft 59 without damaging the system.The drive wheels 47 and 48 drive two endless tapes 62 and 63 of asuitable type such as stainless steel. The drive wheels 47 and 48 arealso formed of a suitable material such as stainless steel. The endlesstapes or belts 62 and 63 travel over a pair of idlers 64 and 66 and thenover large wheel 67. The desired tension is maintained on the tapes 62and 63 by a large idler wheels 68 rotatably mounted on arms 69. The arms69 are pivotally mounted at 71 on the enclosure and each is providedwith a weight at the other end of the arm so that the idler wheels 68are yieldably urged up into engagement with the bottom runs of the tapes62 and 63 whereby the tapes will be driven by the associated drivewheels 47 or 48.

In order to further reduce the space within chamber A, the enclosure 31is formed in such a manner that the bottom wall 74 extends upwardlybetween the two endless tapes 62 and 63 as can be seen particularly inFIGS. 3 and 5. The exit end of the chamber A is provided with aninclined bottom wall portion 74a in which a large pipe 76 is mountedwhich is connected to a source of vacuum (not shown).

The enclosure 31 is provided with an access opening 81 in the top sidewhich is normally closed by a cover plate 82 which is held in place byclamps 83.

A microswitch MS-2 is mounted within the chamber A of the enclosure 31and is provided for a purpose hereinafter described.

As can be seen from FIG. 2, the enclosures 32 and 33 of the coatingapparatus are very similar and for that reason only a detailed view ofthe enclosure 33 is shown in FIG. 6. The enclosure 32 is provided with aremovable cover plate 84. A conveyor assembly 86 of a type similar tothe conveyor assembly 46 is provided within the chamber B of theenclosure 32. A conveyor spacer assembly 88 is mounted within thechamber B of the enclosure 32 and as shown in FIG. 2 is mounted adjacentthe exit end of the chamber B.

The enclosure 33 also includes a removable top cover plate 91. Aconveyor assembly 92 similar to the conveyor assemblies 86 and 46 ismounted within the chamber C.

The enclosure 34 is substantially larger than the enclosures 32 and 33and is provided with a pair of removable cover plates 96. A conveyorassembly 97 is provided which is similar to the conveyor assemblies 46,86 and 92 with the exception that it is provided with additional idlerssimilar to the idlers 64 and 66 in the conveyor assembly 46. A heatedseal duct assembly 98 is mounted in the chamber D at the entrance to thechamber D in line with the top run of the conveyor assembly 97.

An electrical substrate heater assembly 93 (FIG. 6) is mounted withinthe chamber C at the top of the chamber and is of conventional type andis provided for raising the temperature of the substrate to the desiredtemperature for the coating process which is utilized in the apparatus.The heater assemby heats the substrate principally by radiation.

The heated seal duct assembly 98 is formed of a suitable high resistancematerial, such as stainless steel, and is formed to provide a relativelynarrow duct or passage 99 (FIG. 9) which is only just large enough topermit the substrate to pass therethrough without contacting the sealduct assembly 98. The duct 99 serves to provide a high impedance to gasflow in the molecular flow range so that it is possible to createpressure differential from one chamber to another. In the presentembodiment of the invention, these seal ducts are heated to maintain thepre-heat temperature on the glass or other substrate which is introducedin chamber C. Current at a low voltage is supplied to the heated ductassembly 98 through electrical feed-throughs 102 which extend into thechamber D and are connected to the duct assembly 98 as shown in FIG. 9.By making the duct a resistance element itself, it is possible for theduct assembly to serve two purposes. It is readily possible for such aheated duct to provide temperatures as high as 300° C. or above. Thestainless steel which makes up the duct assembly 98 is relatively thinmetal so that there is very little thermal heating required which makesit possible to reach equilibrium conditions rather quickly.

The chamber D can be termed the glow discharge chamber. The seal ductassembly 98 is provided at the entrance of the chamber so it is possibleto maintain an atmosphere of some gas such as oxygen at a fixed pressureof 10 - 40 microns without the pressure being affected appreciably bythe automatic cycling which occurs in chambers A and B as hereinafterdescribed.

By maintaining the chamber D at a predetermined pressure it is possibleto cause glow discharge cleaning of the substrate to take place. Thisglow discharge is accomplished by glow discharge electrode assemblies106 which are spaced longitudinally on the chamber D. Such glowdischarge assemblies are substantially conventional and generallyconsist of a T-shaped housing 107 which has an electrode 108 mountedtherein. The electrode shield 109 is mounted on the housing and servesto direct the glow discharge. Each glow discharge assembly 106 isprovided with a terminal 111 which is adapted to be connected to asource of high voltage.

Chamber E (FIGS. 10 and 11) which follows chamber D is divided up intofour separate smaller chambers 116. The smaller chambers 116 are allaccessible through a common cover plate 117 which forms a part of theenclosure 35 which forms the chamber E. Each of the individual chambers116 of the chamber E is provided with an individual pump to obtain thedesired pressure. In general, the pumps are operated so that thepressure progressively decreases in the chambers 116 from the left tothe right of chamber E. Each of the chambers 116 is provided with anelectrically heated seal duct assembly 118 which is identical to theheated seal duct assembly 98 hereinbefore described. The seal ductassemblies 118 are electrically isolated from the enclosure forming thechamber E and are heated by resistance heating so that the duct itselfcan transfer radiant energy to the substrate which is to be coated.

As can be seen particularly from FIG. 10, an endless conveyor assembly119 for the chamber E is provided for moving the substrates which are tobe coated in the apparatus through the chamber E. The conveyor assembly119 consists of a motor 121 which is mounted upon a speed reducer 122.The speed reducer 122 is mounted upon a base 123 which is secured to theframework 29. The speed reducer 122 drives a sprocket 124 which drivesan endless chain 126. The chain 126 drives a plurality of sprockets 127which are mounted upon shafts 128. The shafts 128 extend through rotaryfeed-throughs 129 mounted upon the framework 29 and drive pairs ofrollers 131 mounted on opposite sides of each of the chambers 116 in thechamber E. The rollers 131 are interconnected by connecting shafts 132.As can be seen from FIGS. 10 and 11, one pair of rollers is provided ineach of the chambers 116 adjacent the exit end of the seal duct assembly118 positioned therein. A chain-tightening sprocket assembly 136 ismounted on the framework 29 and is provided for maintaining the chain126 in a relatively tight condition as particularly shown in FIGS. 10and 11.

Chamber F follows the chamber E. The enclosure 36 which forms thechamber F is also provided with a removable cover plate 141 to permitaccess to the chamber. The framework 29 is provided with an additionalenclosure 142 which is in communication with the enclosure 36 as shownin FIGS. 12 and 13. The enclosure 142 is provided with a large opening143 which is in communication with a large vacuum pump 144 of aconventional type. A heated seal duct assembly 146 is mounted at theentrance to the chamber F within the enclosure 36 of a type similar tothe heated seal duct assembly 98. An additional unheated seal ductassembly 148 is provided in the chamber F and is mounted at the exit endthereof.

One end of an endless conveyor system 151 is mounted within the chamberF for advancing the substrates from the chamber F into the subsequentchamber G and will be described hereinafter.

Chamber G can be characterized as the main coating chamber which isformed of a plurality of sections or smaller chambers 153, each of whichis provided with a removable cover plate 154. The number of sections orseparate compartments in this main coating chamber G is determined bythe number of successive layers it is desired to deposit upon thesubstrate. Thus, in the present embodiment of the apparatus, there areprovided six separate chambers 153 for depositing six layers on thesubstrate.

Each of the sections 153 is provided with an unheated seal duct assembly156 at the entrance end of the section and a similar assembly at theexit end of each section.

Any one of the sections 153 may be provided with a substrate heatingsystem similar to that provided in chamber C mounted on the cover plate154 for the purpose of heating the substrate. Heating may be carried outduring coating or between application of coating layers if the heatingfunction is substituted for the coating function in one or moresections.

As can be seen particularly from FIGS. 12 and 14, the enclosure 37 forthe chamber G has a substantially greater depth than the precedingchambers. An additional enclosure 158 is provided for each of thesimilar chambers 153 within the chamber G and is in communication withthe smaller chamber 153. Each section or smaller chamber 153 is providedwith its own pressure control system. Thus, as shown, each is providedwith its own vacuum pump 159 which is in communication with a largeopening 161 provided in the enclosure 158.

Each of the smaller sections or chambers 153 is provided with its ownevaporation source 163. The evaporation source can be of any suitabletype. By way of example, as shown in the drawing, the evaporationsources 163 can be of the type described in U.S. Pat. No. 3,619,840. Aspointed out therein, such evaporation sources are of the type whichutilize an electron gun to evaporate or vaporize the material which isto be utilized for the particular layer on the substrate.

Shielding means is provided for each of the evaporation sources 163 andconsists of a removable four-sided shielding structure 166. theshielding structure 166 is formed of suitable good heat conductingmaterial such as sheet copper in which each of the four sides is formedwith a vertical side wall 167 and an inwardly inclined side wall 168.The inclined side walls 168 are formed so that there remains arectangular opening 169 immediately overlying the central part of theevaporation source 163 as can be seen particularly in FIG. 15. Theshielding structure 166 is provided with four legs 171 on the corners ofthe same so that the lower extremities of the walls 167 are positionedabove the bottom wall of the enclosure 37. The shielding structure 166also includes means for providing suitable cooling as, for example,tubing 172 welded on the outer surfaces of the walls 167 and 168 asshown particularly in FIG. 16. During operation of the apparatus,cooling water is passed through the cooling coils 172.

The shielding means also includes a shielding member 176 which has asize which is sufficiently large to cover the opening 169. It also canbe called a spatter shield. This shielding member 176 is mounted upon anarm 177 which is pivotally mounted in a sleeve 178 secured to theenclosure 37. Means is provided for moving the shielding member 176 froma position in which it overlies the shielding structure 166 and coversthe opening 169 in an out-of-the-way position such as that shown in FIG.15 and consists of lever means (not shown) of a conventional type.

Each section or chamber 153 of the coating chamber G is provided with anevaporation rate monitor 186 of a suitable type, for example, anevaporation rate monitor of the type described in U.S. Pat. No.3,773,548 can be utilized herein. The evaporation rate monitor 186 isadapted to receive a small portion of the evaporated stream of materialpassing up through the opening 169 in the shielding structure 166through an opening 187. As hereinafter explained, the evaporation ratemonitor 186 is utilized for controlling the rate of evaporation from theevaporation source 163.

Each of the sections or chambers 153 is also provided with means forcontrolling the distribution of the coating material on the glass orother substrates so that a uniform distribution is obtained Such meansconsists of a shielding assembly 191. As shown particularly in FIGS. 18and 19, such shielding assemblies consist of a support member 192 whichis secured to the framework 29 within the chamber. As can be seenparticularly in FIG. 18 the support member 192 extends horizontallyacross the chamber. A pair of U-shaped brackets 193 are mounted onopposite ends of the support member 192 and have a pair of sleeves 194mounted thereon in such a manner that they face each other. A rod 196extends through the sleeves 194 and has mounted thereon another sleeve197 which extends in through the sleeves 194. A collar 198 is slidablymounted on each of the sleeves 197. A Z-shaped plate 199 is secured tothe two collars 198 and is also slidably mounted upon the sleeve 197. Ashielding member 201 is secured to the Z-shaped plate or member 199 bysuitable means such as screws 202. The shielding member is provided withan arcuate convex forward edge 203 which extends in a directionlaterally of the chamber.

Means is provided for advancing the shielding member 201 into thechamber in which it is mounted and consists of an internally threadedsleeve 206 which is secured to the Z-shaped member 199. A threaded rod207 is threaded into the sleeve 206 and is connected by a coupling 208to the output shaft 209 of a right-angle gear unit 211. The gear unit211 is mounted upon a bracket 212 secured to the support member 192. Theinput shaft 213 of the gear unit is connected to a universal joint 214.The universal joint 214 is connected by a shaft 216 to another universaljoint 217. The joint 217 is connected to another shaft 218 which extendsoutside of the enclosure in which it is mounted where it is adapted tobe engaged by a crank (not shown) so that by rotation of the shaft 216,the shielding member 201 can be extended or retracted to the desiredposition.

As can be seen from FIG. 2, the same endless conveyor advancing assemblyis provided throughout the main coating chamber G and extends into thechamber H. The construction of the enclosure 38 for the chamber H isvery similar to that for the enclosure 36 for the chamber F. Thus, it isprovided with a removable cover plate 221. It is also provided with aseal duct assembly 222 which corresponds to the unheated seal ductassembly 148 in the chamber F. However, it is provided with a watercooled seal duct assembly 223. The purpose of the water cooling on theduct is to provide a means of cooling the glass substrate by radiationso as to reduce the thermal shock when exiting to atmosphere. As can beseen from FIG. 2, the endless conveyor assembly 151 also extends intothe chamber H. The endless conveyor assembly 151 is similar to the oneshereinbefore described. It is provided with a pair of driving rollers226 which are driven by an electric motor and speed reducer (not shown)of the type hereinbefore described. The driving rollers 226 areinterconnected in the same manner as the other endless conveyorshereinbefore described. They drive two endless tapes 227 formed of asuitable material such as stainless steel. As can be seen, the tapes 227travel over rollers 228 in the chamber H and then travel over rollers229 and under rollers 231 in each of the sections 153 of chamber G. Thetapes then travel over rollers 232 in chamber F and around a roller 233in chamber F. The rollers 232 and 233 are rotatably mounted intape-tightening assemblies 234. A pair of additional small rollers 236are provided on each of the sections 153 of the chamber G adjacent therollers 229 as shown particularly in FIG. 16.

From the arrangement which is shown in FIG. 2, it can be seen that theupper run of the tapes 227 are supported by the smaller rollers 236 andby large rollers 231 intermediate the same. It can be seen that at theentrance and exit ends of each of the sections 153 of the chamber G thatthe upper and lower runs of the tapes are brought together so that theycan travel through the relatively shallow unheated seal duct assemblies156.

The chamber I which is next to the chamber H is divided into twosections 241. A common removable cover plate 242 is provided as a partof the enclosure 39 for the chamber I. Water cooled seal duct assemblies243 are provided on the exit end of the sections 241 and are similar tothe water cooled seal duct assemblies 223 provided in section H. Aconveyor assembly (not shown) very similar to that which is utilized inchamber E is provided within the chamber I.

Chamber J which follows chamber I is very similar to chamber B. Theenclosure 40 for this chamber includes a removable cover plate 246. Italso includes a conveyor assembly 247 mounted within the chamber whichis substantially identical to the endless conveyor assembly 86 providedin chamber B. A gate valve V3 is provided at the exit end of the chamberJ and is identical to the valve V2 provided at the entrance end ofchamber B. Chamber K which follows the gate valve V3 is substantiallyidentical to chamber A. The enclosure 41 for this chamber is providedwith a removable cover plate 249. It is also provided with an endlessconveyor 251 which is substantially identical to the endless conveyor 46provided in chamber A. A gate valve V4, similar to the gate valve V1, isprovided at the exit end of the chamber K. An endless conveyor assembly252 is provided on the exit side of the valve V4 and is adapted tosupply the substrates as they exit from the chamber K into a downelevator assembly 253. Microswitches (not shown) are provided in chamberJ. Their positions and functions are hereinafter described.

A portion of the conveyor spacer assembly 88 which is shown in chamber Bis shown in detail in FIG. 17. As shown therein, it consists of a lamphousing 261 having a plurality of bores 262 extending therethrough. Alamp socket 263 is mounted within each of the bores and is adapted toreceive a lamp 264. The lamp housing 261 is mounted upon upper and lowercooling blocks which have cooling channels (not shown) provided thereinwhich are in communication with tubes 268. A lamp socket cover 269 ismounted on the upper cooling block 266 and on lamp housing 261. Aprinted circuit board housing 271 is mounted upon the lower coolingblock 267 and has mounted therein a printed circuit board (not shown)which carries the circuitry as hereinafter described for the conveyorspacer assembly 88. A cover plate 272 is provided for covering theprinted circuit housing 271. A spacer block 273 is secured to the lamphousing 261 and has mounted thereon, by suitable means such as screws274, upper and lower aperture plates 276 and 277. As can be seen, theaperture plates are spaced and parallel and are provided with aplurality of apertures or openings 278 which are arranged in two rows insuch a manner that the apertures in the top plate 276 are inregistration with the apertures in the bottom plate 277. The apertures278 in the aperture plates 276 and 277 are arranged so that with theapertures in the two rows being offset with respect to each other thatthere are in effect 47 light beams created thereby utilizing the lightfrom the lamps 264. The 47 holes are placed in two separate rows so thatthere will not be interference between one photocell to the next. Eachof these light beams is adapted to light a photocell carried by theprinted circuit board housing 271. Each photocell forms a part of theelectrical circuit carried by the printed circuit board mounted in theprinted circuit housing.

The upper and lower plates 276 and 277 form a collimating system foreach of the 47 light beams which are provided. The combination of thelamp housing block 261, the top aperture plate 276 and a lamp cover (notshown) form a light integrating chamber which uniformly illuminates the47 holes in the top aperture plate. Because an integrating light chamberis utilized, approximately 20 to 30% of the lamp bulbs which areutilized can burn out without degrading the operation of the system.

A U-shaped recess 281 is provided between the lower aperture plate 277and the top of the printed circuit board housing 271 and is of such adimension that it is able to receive and permit rectangular frames 286to pass therethrough. The frames 286 can be formed of any suitablematerial such as aluminum. As can be seen from FIG. 17, the frames 286are provided with a rectangular recess 287 in the upper surface adjacentthe inner margin of the frame which is sized so that it is adapted toreceive the glass substrate 288 which are to be coated in the apparatus.

The circuitry which is used is provided on a printed circuit board (notshown). The printed circuit board is mounted in the printed circuitboard housing 271 and forms a part of the conveyor spacer assembly shownschematically in FIG. 20.

The overall apparatus includes additional electronics much of which isconventional and which is represented in FIG. 1. Thus, there areprovided a plurality of consoles 291, one for each of the sections 153of the chamber G for controlling the operation of the evaporationsources 163 hereinbefore described. Similarly, there are providedadditional control consoles 292 and 293 for automatically controllingother portions of the apparatus as hereinafter described.

The conveyor spacer assembly 88 is water-cooled so that it can bereadily operated within a vacuum chamber as, for example, the chamber B.

Operation of the multi-layer coating apparatus and system in performingthe present method may now be briefly described as follows. Let is beassumed that it is desired to coat a plurality of substrates ofrelatively large size with the multi-layer coating apparatus and system.By way of example, let it be assumed that the substrates are glass andthat they have been pre-cut to a predetermined size as, for example,323/4 by 503/4". With such a size, it is possible to provide finishedcoated pieces of glass which have a size 30 inches × 48 inches. Thesheets of glass are passed through a washing machine which may be of aconventional type which washes both sides of the glass and rinses thesame. Thereafter, the remaining moisture on both sides is blown off. Itis the bottom side of the glass that is to be coated. This surface willnot be touched during passage through the apparatus, as hereinafterdescribed, by rollers conveyor belts and the like. With the glass dryand at a temperature ranging from 80° to 90° F., the glass substratesare loaded into frames 286 which are positioned in a horizontal mannerand with the glass placed in the recesses 287 provided in the frames.The glass in the frames 286 is loaded into an elevator (not shown) andraised so that it can be moved onto the inlet conveyor 27 where it is ina position to be introduced into the entrance chamber A.

When the apparatus is ready to receive the next sheet of glass mountedof the frame 286, the valve V1 is opened, and the conveyor 27 is placedin operation. The frame 286 bridges the gap through the entrance valveV1 and moves at a relatively rapid rate as, for example, a rate of 72ft. per minute. As soon as the frame 286 strikes the microswitch MS-2,the endless conveyor 46 within the chamber A is stopped. Thereafter, thegate valve V1 is closed and the pumping system for chamber A isimmediately actuated and the chamber is pumped down relatively rapidlyto a suitable pressure as, for example, 50 microns. As soon as thispressure is attained in chamber A and the first of the 47 light beams,in the conveyor spacer assembly 88, is clear the valve V2 opens. Theendless conveyors 46 and 86 in the chambers A and B are then started andtravel at approximately the same rate of speed as, for example, 72 ft.per minute. The frame 286 is thus passed quickly from chamber A intochamber B. This movement continues until the frame from chamber Aclosely approaches the last frame which previously had entered intochamber B. As herein after explained, this last frame 286 in chamber Bwhich preceded the frame being moved from chamber A is moving at a muchslower predetermined rate of speed as, for example, a rate from 2 to 4ft. per minute depending upon the process parameters being utilized. Inorder to prevent the frame which is leaving chamber A from bumping intothe rear end of the preceding frame, the conveyor spacer assembly 88 isprovided which automatically controls the conveyor in chamber B so thata predetermined space is provided between the frames as, for example, aspace of one-half inch. When the proper spacing has been obtained, thenthe conveyor in chamber B will be slowed down so that the frame whichhas been advanced out of chamber A will continue through the chamber Bat the same rate of speed that the preceding frame is being advanced.From this point on, the frame which has been advanced out of chamber Awill follow the preceding frames and will travel at the same rate ofspeed as the preceding frames until near the exit end of the apparatusas hereinafter described

In other words, it can be seen that the purpose of the conveyor spacerassembly is to adjust the spacing between two frames travelling atdifferent speeds on two conveyors within an apparatus to a predeterminedspacing and then to adjust the speed of one of the conveyors to matchthe speed of the other conveyor so that the predetermined spacing willremain constant thereafter.

In the conveyor spacer assembly which is shown in detail in FIGS. 17 and20, the printed circuit in housing 271 supplies zero volts out when thephotocell is illuminated by its light beam. Thus, the photocell with itsassociated circuitry can be termed a digital gate as shown in FIG. 20.Thus, there are provided digital gates numbered from 1 - 47. The portionof this assembly which measures the spacing between two frames 286 isthe digital gates 2 - 47 and their associated photocells, light beamsand the like. The output of the digital gates 2 - 47 are fed into ananalog summer 301 with a gain of K. The function of this analog summeris to supply an output voltage which is proportional to the number ofcells 2 - 47 that are illuminated. The gain of K is such that the outputis approximately 10 volts when all of the cells 2 - 47 are illuminated.When all the cells 2 - 47 are dark, the output of the analog summer 301is zero volts. If half of the cells are illuminated, the output is 5volts, and so on. Thus, it can be seen that the output of the analogsummer 301 changes in increments equal to 1/46 of 10 volts and that novoltages between these increments are obtainable. This is because theoutput of the digital gates 2 - 46 is either zero or -30 volts. A stepvariable reference 302 is provided which consists of a voltage dividerwhose output can be changed in increments equal to the 46 output levelsof the analog summer. This variable reference 302 is used to adjust thespacing between the leading frame and the trailing frame entering theconveyor spacer assembly 88.

The output of the analog summer 301 is supplied to a comparator 302which receives its reference from the variable reference 302. When theoutput level of the analog summer 301 is greater than the output fromthe variable reference 302, the output of the comparator is onepredetermined value and when the output of the analog summer 301 is lessthan the output of the variable reference 302, the output of thecomparator 302 is a different predetermined value as, for example, thetwo values can be -15 volts and +15 volts approximately, respectively.

The photocell No. 1 operates a digital gate No. 1 in the same manner inwhich digital gates No. 2 - 47 are operated. The outut of digital gate 1supplies its output to a buffer amplifier 303. The output of bufferamplifier 303 is supplied to a relay 304. Relay 304 is energized whenthe light beam is shining on photocell 1 and is deenergized when thephotocell 1 is dark. Relay 304 supplies a -15 volts to an OR gate 306when the relay 304 is energized and supplies zero volts to the OR gate306 when the relay 304 is deenergized. The output of the comparator 302supplies the second input to the OR gate 306. The output of the OR gate306 is supplied to a buffer amplifier 307 and the output of the bufferamplifier 307 is supplied to a relay 308. Relay 308 is energized wheneither of the two inputs to the OR gate 306 is at a predeterminedvoltage as, for example, a -15 volts. Relay 308 will be deenergized whenboth the inputs to the OR gate 306 are at zero volts or positive. Theoutput of the relay 308 is connected to a motor control 309 which isconnected to the motor 49 for the conveyor assembly 86 in chamber B.

When the relay 308 is energized, the conveyor 86 runs fast and whenrelay 308 is deenergized, conveyor 86 runs slow. When conveyor 86 isrunning slow, it is running at the same speed as conveyor 92. Theconveyor 92 always runs slow. By way of example, when conveyor 86 isrunning fast, it must run fast enough so that trailing frame 286 whichis carried by it will travel at least 5 ft. in the same amount of timethat it takes the leading frame 286 on the conveyor 92 to travelapproximately 1 ft. This is necessary because the leading frame 286 isapproximately 5 ft. ahead of the trailing frame 286 when the trailingedge of the leading frame 286 has travelled past the light beam forphotocell 1.

Let it be assumed to further explain the operation of the conveyorspacer assembly 88 that the apparatus is operating but there are noframes on the conveyor system. When the first frame 286 carrying asubstrate enters onto the conveyor 86 in chamber B, the conveyorassembly 86 will be operating in the fast mode because all of the lightbeams 1 - 47 are illuminating their respective photocells 1 - 47. Assoon as the leading edge of the frame 286 passes through light beam No.1, photocell No. 1 will be darkened and relay 304 will be deenergized.Relay 304 supplies one of the inputs to the OR gate and this input willbe zero. However, the other input to the OR gate is a logic one or a -15volts and, therefore, the output to the OR gate will be a logic one andcause the motor for the conveyor 86 to continue running fast.

At this time the desired spacing to be used between the frames is chosenand this is set into the system by adjusting the variable reference 302in the manner hereinbefore described. By way of example, the desiredspacing can be anything from zero to a predetermined dimension as, forexample, 113/4 inches. Let it be assumed that a spacing of one inch isdesired which would be equivalent to all but four of the light beamsbeing covered by the frames 286 as they are being advanced through theapparatus.

As the leading edge of the first frame 286 continues to travel throughthe light beams until all but the last four light beams, that is, lightbeams 44-47 are blocked, then the output of the analog summer 308 willdrop below the reference level from the reference 302 and the output tothe comparator will go to a + 15 volts which is a logic zero for the ORgate 306. At this time, both inputs to the OR gate will be a logic zeroand relay 308 will be deenergized causing the motor 49 to transfer fromhigh speed to low speed operation. Thereafter the first frame 286 willcontinue to travel through the remaining light beams of the conveyorspacer assembly 88 at slow speed. When the trailing edge of the firstframe No. 286 clears the light beam No. 1, light will illuminatephotocell No. 1 causing relay 304 to be energized. When relay 304 isenergized, a logic one will be fed into the OR gate 306 which causes alogic one to be supplied to the relay 308 to energize it and to causethe conveyor 86 to transfer back to high speed operation.

When relay 304 is energized, and assuming that the other conditionsrequired in the apparatus have been met, the valve V2 will open and ashereinbefore described, the conveyor assembly 46 in chamber A will beplaced in operation to rapidly advance the frame carrying a substrateonto the conveyor assembly 86 in chamber B which is travelling at itsfast speed. The frame 286 which it is carrying will catch up rapidlywith the preceding frame 286 which is being carried by the conveyorassembly 92 and before the trailing edge of the preceding frame 286leaves the conveyor spacer assembly 88. When the leading edge of thetrailing frame 286 passes through light beam No. 1, photocell No. 1 willbecome dark and relay 304 will be deenergized thus causing one of theinputs to the OR gate 306 to go to a logic zero. However, since thepreceding frame 286 has travelled more than four light beams that werechosen previously by the time the trailing frame passes through lightbeam No. 1, the other input to the OR gate 306 will be at a logic oneand relay 308 will be energized. Thus, the motor 49 for the conveyor 86will continue running in its fast mode. This will continue until allexcept any four of the photocells are illuminated. At this time, theoutput of the analog summer 301 will drop below the reference levelsupplied by the reference 302 and the other input to the OR gate 306will be logic zero. At this time both inputs to the OR gate 306 are atlogic zero which will cause relay 308 to be deenergized and the motor 49for the conveyor 86 to transfer to slow speed operation which, aspointed out previously, is the same speed as the speed of the conveyorassembly 92. Thereafter the preceding and trailing frames 286 willtravel at the same rate of speed with a one inch spacing between thesame. When the trailing edge of the trailing frame 286 passes throughlight beam No. 1, conveyor 86 will again transfer to fast speedoperation and trigger another frame to be advanced from chamber onto theconveyor 86. This next frame will be advanced at high speed until itcomes within one inch of the preceding frame, at which time the conveyor86 will return to slow speed operation in the manner hereinbeforedescribed.

Thus, it can be seen that conveyor spacer assembly 88 prevents theframes from bumping into each other and makes it possible to rapidlyaccelerate frames out of chamber A so that valve V2 need only remainopen for very short periods of time. In addition, the conveyor spacerassembly makes it possible to maintain uniform predetermined spacingbetween each of the frames so that the process parameters can be readilycontrolled.

It will be noted that the conveyor spacer assembly 88 utilizes a digitalapproach which is quite precise in its operation.

After a frame has been advanced from chamber A in the mannerhereinbefore described and the leading edge of the frame 286 hasinterrupted the first of the 47 light beams, in the conveyor assembly 88the gate valve V2 closes. Chamber A is then vented to the atmosphere.Valve V1 is opened and the next frame is advanced into chamber A. Thecycle hereinbefore described is then repeated.

During operation of the apparatus, it is desirable to keep the vacuum inchamber B at an average which is about 10 microns. Chamber C is alsomaintained at this average vacuum.

As the frame 286 with the glass substrate 288 is carried into chamber C,the glass is heated in this chamber to the temperature or slightly abovethe temperature at which it is desired to maintain the glass substrate288 during the coating process. This heating is accomplished by theglass heater assembly 93 mounted at the top of chamber C. This heaterassembly causes the heat to radiate downwardly onto the glass. It isimportant that the glass substrate in the chamber C be heated to atemperature which is at least slightly above any temperature which willbe encountered during the remainder of the process. This will ensureproper outgassing of the glass and the frame in chamber C so thatfurther outgassing will be reduced in the subsequent chambers.

As the glass substrate 288 and the frame 286 carrying the same is slowlyadvanced through the chamber C, it is heated and then it passes into thechamber D through the first heated seal duct assembly 98 mounted at theentrance to the chamber. As pointed out previously, this heated sealduct assembly is provided with a relatively narrow slot 99 so as to makeit possible to maintain a pressure differential between chambers C and Dand the gasses which are present in chamber D. Chamber D can beidentified as the glow chamber and may have an atmosphere of a certaingas such as oxygen therein at a fixed pressure ranging from 10 - 15microns which corresponds to 1 - 5 × 10.sup.⁻² torr. It is desirablethat this pressure be not unduly affected by the automatic cycling whichis occurring at chamber A and B of the apparatus. In other words, it isvery desirable that chamber D be maintained at a constant predeterminedpressure so that glow discharge cleaning of the underside of the glasssubstrate 288 can take place within chamber D. The glow dischargecleaning takes place in the conventional manner by the plurality of glowdischarge electrode assemblies 106 provided within the chamber D. Itwill be noted that the chamber D is twice the length of chamber C. Thisis desirable because the glass substrates move through the chamber C andD at the same rate of speed and it requires a longer period of time forglow discharge cleaning of the glass substrate than it does for heatingof the glass substrate.

After glow discharge cleaning, the glass substrate 288 is ready to beintroduced into the high vacuum portion of the apparatus for treatmentfor application of the coatings. During passage through the chamber D,it is possible that the temperature of the glass may have droppedslightly and it may, therefore, be necessary to further heat the glassto bring it up to the desired temperature. Also, the pressure within thechamber D is too high for subsequent processing steps and, therefore, itis necessary to reduce the pressure. This is accomplished in the chamberE which, as explained previously, is provided with four separatechambers 116, each of which is provided with a heated seal duct assembly118. As explained previously, each of these chambers 116 is individuallypumped and the pressure is gradually brought down in the four chambers116 until the pressure has been reduced to approximately 1 × 10.sup.⁻⁶torr. During the time that the glass substrate is passing through thechamber E, it is heated by the heated seal duct assemblies 118 so thatthe glass substrate 288 is brought up to and maintained at the desiredtemperature.

The chamber F which precedes the chamber G and the chamber H whichfollows the chamber G are both maintained at a pressure which is thelowest in the entire apparatus and should be lower than the pressure inthe chamber G so that there always is a gas flow from chamber G tochambers F and H. In this way, it is possible to positively control thecomposition of the gas of the six coating chambers 153 provided in thesection G. The chambers 153 in section G are maintained at apredetermined pressure ranging from 1 × 10.sup.⁻⁴ to 1 × 10.sup.⁻⁶ torr.By starting with a pressure in one of the chambers 153 and then adding agas to the system to raise the pressure, it is possible to control theenvironment within the chamber very closely. Since six of the chambers153 have been provided, it is possible to apply from one to six layersof various types of coating on the glass substrate 288 in one passthrough the apparatus. This is possible because each of the chambers 153is separately pumped as hereinbefore described. It is also provided withan evaporation source 163 and an evaporation rate monitor 186. Duringoperation of the apparatus, the evaporation source is operated and thevapor streams emanating therefrom pass upwardly through the shieldingstructure 166 onto the bottom surface of the glass substrate 288. Theamount of coating material is monitored by the evaporation rate monitor186 and this automatically controls the rate of evaporation from theevaporation source so that the desired thickness of the layer beingdeposited on the substrate is obtained. In order to obtain a uniformdistribution across the bottom of the glass substrate, the shieldingassemblies 191 provided in each of the chambers 153 is utilized. Theshielding member 201 can be extended or retracted to obtain the desireduniformity.

The thickness of the coating layer being deposited upon the glasssubstrate can be varied by changing the rate of travel through thechamber. However, since it is desirable to maintain a uniform rate oftravel through all of the chambers, the thickness of the coatings arecontrolled by the rate of evaporation from the source which can bevaried as desired and controlled by the evaporation monitor 186.

When the glass substrate 288 is passed through the last of the coatingchambers 153, it passes into the chamber H, the purpose of which wasexplained previously, after which it passes into chamber I. Chamber I isdifferentially pumped in two sections. The seal ducts are utilized formaintaining this differential in pressure. After passing through chamberI, the glass substrate passes into chamber J towards the gate valve V3.When the exit chamber K has been cleared and is ready to receive thenext frame 286 with a glass substrate thereon, the apparatus isautomatically cycled to open valve V3. As soon as the valve V3 isopened, the conveyor assembly 247 is operated at a high rate of speed toadvance the same onto the conveyor 251 in chamber K. Means is providedfor stopping the frame 286 within the chamber K when it is within thechamber K. The valve V3 is closed and thereafter the chamber K is ventedto the atmosphere. Valve V4 is then opened and the frame 286 and theglass 288 carried thereby are rapidly advanced out of chamber K byoperation of the conveyor 251 onto the exit conveyor 252, after which itis delivered to a down elevator 253. The frame 286 with the glasssubstrate 288 is then lowered and thereafter the glass substrate isseparated from the frame. The glass can then be cut to remove theuncoated outer margins which were covered up by the frame. The framesare returned to the other end of the apparatus and are ready for loadingand re-use in the apparatus.

It will be noted that fewer seal ducts are required at the exit end ofthe apparatus than at the entrance end. This is because at the entranceend, the principal gas load is from the glow discharge chamber, thusrequiring additional pumping at the end and additional seal ductassemblies.

It is apparent from the foregoing that a unique multi-layer coatingapparatus, system and method has been provided. The arrangement of theapparatus is such that the glass substrate is heated prior to glowdischarge cleaning. If the glow discharge cleaning has occurred first,the subsequent heating could possibly affect the cleaned surface on theglass which had been prepared.

There is ample provision in the apparatus for heating the substrate andfor maintaining the substrate at the desired temperature. The apparatusalso has the advantage that there is provision for heating betweenlayers so that layers can be applied at different temperatures.

During processing in the apparatus, the glass substrate which is beingcoated travels in a horizontal position with the surface being coatedfacing downwardly. This is very desirable because this bottom surfaceremains much cleaner because material cannot fall down on it from thetop. The horizontal mounting of the substrates is also advantageousbecause it is easier to provide a source in which the vapor streams passupwardly from the source. In addition, it is possible to obtain a sourcewhich will provide a more symmetrical distribution. Also, it is moreadvantageous to evaporate many materials particularly from an electrongun source where materials are generally disposed in parallel to thesurface which is to be coated.

The apparatus has the advantage in that if coating materials do build upupon the interior of the chambers, such material can fall off withoutaffecting the bottom surface of the substrate which is being coated. Theshielding structure 166 prevents any material which falls off fromfalling back into the source.

The relatively narrow or shallow conveyors which are utilized make itpossible to use relatively small segregation valves in the form of thevalves V1, V2, V3 and V4. There is no necessity for a large opening. Allthat is required is a narrow opening for the frame which carries thesubstrate which is to be coated. For the main coating chamber G and thechambers F and H on opposite sides of the same, there is only oneconveyor system which makes it necessary to only drive this conveyorsystem from one end. The desired flexibility is still retained withoutthe disadvantages of outgassing during heating.

The heated seal ducts perform two functions in that they provide thedesired sealing and at the same time provide a means for heating thesubstrates to the desired temperature.

We claim:
 1. In a multiple layer coating apparatus for coatingsubstrates carried by frames disposed in generally horizontal positions,means forming at least one coating chamber, a vertically disposedcoating material source in the coating chamber for vaporizing at leastone material for carrying out coating operations in the coating chamberwhereby the vaporized material moves upwardly, means forming an entrancechamber in communication with the coating chamber, means forming an exitchamber in communication with the coating chamber, valve means disposedat opposite ends of each of the entrance and exit chambers for sealingsaid entrance and exit chambers and interrupting communication with saidcoating chamber, means for creating a vacuum condition in the coatingchamber, a separate driven conveyor assembly provided in each of theentrance chambers, the coating chamber and the exit chamber forreceiving and advancing the frames and substrates therethrough so thatthe frames carrying the substrates and the substrates are maintained ina generally horizontal position in at least the coating chamber with thebottom sides of the substrates being exposed to the vapor stream fromthe source, said driven conveyor assembly in the coating chamber havinga horizontal supporting surface upon which said frames are adapted torest during travel through the coating chamber, said separate drivenconveyor in said coating chamber being driven at a substantially uniformslow speed, said valve means being movable to open positions to permitsaid frames to pass therethrough, said separate driven conveyorassemblies in said entrance chamber and said exit chamber being capableof being driven at a fast speed in comparison to said slow speed andframe spacing means including means having a plurality of sensingelements in excess of two adapted to be actuated by the frames forsensing the spacing between frames for controlling the operation of theconveyor assemblies whereby a frame is moved rapidly out of the entrancechamber toward the coating chamber until a predetermined spacing existsbetween it and the preceding frame for maintaining a predeterminedminimum spacing between the frames during their travel through thecoating chamber.
 2. Apparatus as in claim 1 together with means formingan additional chamber between said entrance chamber and said coatingchamber and additional conveyor means mounted in said additional chamberoperable at a fast speed and at a slow speed with the fast speedcorresponding to the speed of the conveyor assembly in the entrancechamber and with the slow speed corresponding to the speed of theconveyor assembly in the coating chamber, and wherein said frame spacingmeans includes means for sensing when a predetermined spacing existsbetween the frames to cause the additional conveyor assembly to changefrom a fast speed of operation to a slow speed fo operation. 3.Apparatus as in claim 1 together with means forming a heating chamberdisposed prior to the coating chamber for receiving substrates carriedby the frames, means in the heating chamber for heating the substratescarried by the frames prior to entrance into the coating chamber andmeans for glow discharge cleaning the substrates after the substrateshave been heated.
 4. Apparatus as in claim 1 together with an additionalchamber disposed on each of the opposite ends of the coating chamber andbetween the entrance and exit chambers and through which the carriersand substrates pass, the additional chambers being normally maintainedat a pressure which is lower than the pressure in the coating chamberand the entrance and exit chambers so that there is a flow of gas out ofthe coating chamber in both directions.
 5. Apparatus as in claim 1wherein said coating material source in the coating chamber forvaporizing at least one material is in the form of a single source. 6.Apparatus as in claim 1 wherein a plurality of serially arranged coatingchambers are provided together with a vertically disposed coatingmaterial source in each coating chamber, means in certain of saidcoating chambers for heating the substrate, an evaporation rate monitorin each coating chamber for controlling the rate of evaporation from thesource in that coating chamber and seal duct means mounted between saidentrance chamber and the first coating chamber in series and and saidexit chamber and the last coating chamber in the series so that apressure differential can be maintained between said coating chambersand the other chambers whereby leakage with respect to the coatingchambers can occur only outward from the coating chambers.
 7. Apparatusas in claim 6 wherein said seal duct means includes means for supplyingheat to the substrate at the same time that the substrate is passingthrough the seal duct means.
 8. Apparatus as in claim 6 wherein at leastcertain of said coating chambers are provided with masking means, saidmasking means being adjustable for movement in a direction which isparallel to the path of travel of the substrates through the apparatus.9. Apparatus as in claim 5 together with means in the coating chamberfor shielding the source in the coating chamber, said means forshielding including a shielding structure surrounding the source, theshielding structure having an opening overlying the source, said meansfor shielding also including a shielding member having a size largerthan said opening, and means for moving said shielding member between aposition overlying said opening and an out-of-the-way position. 10.Apparatus as in claim 8 wherein said masking means includes ahorizontally disposed shielding member having an arcuate edge whichextends laterally of the chamber, together with means for causingrectilinear movement of said shielding member in said coating chamber ina direction parallel to the path of travel of the substrates in thecoating chamber and between the substrates and the source.
 11. Apparatusas in claim 1 wherein said means having a plurality of sensing elementsin excess of two adapted to be actuated by the frames for sensing thespacing between the frames includes means forming a plurality of lightbeams disposed in the path of travel of the frames so that the lightbeams are interrupted by the frames as they are advanced, means forsensing the presence or absence of at least certain of the light beams,comparator means, means connecting said comparator means to said meansfor sensing the presence or absence of light beams, variable referencemeans connected to said comparator means for supplying signals havingpreselected levels to said comparator means, said comparator meansdetermining whether the signal from the reference means is greater orless than the signal from the means for sensing the presence or absenceof light beams and supplying a signal for controlling the operation ofthe conveyor assemblies.
 12. In a multi-layer coating apparatus forcoating substrates carried by frames disposed in generally horizontalpositions, means forming at least one coating chamber, a coatingmaterial source in the coating chamber for vaporizing at least onematerial for carrying out coating operations in the coating chamber,means forming an entrance chamber, means forming an exit chamber, valvemeans disposed at opposite ends of each of said entrance and exitchambers, means for creating a vacuum condition in the coating chamber,a separate conveyor assembly provided in each of the entrance chamber,the coating chamber and the exit chamber for receiving and advancing theframes and substrates sequentially therethrough with the frames, and thesubstrates being maintained in a generally horizontal position in atleast the coating chamber with the bottom sides of the substrates beingexposed to the vapor stream from the source, frame spacing means forcontrolling the operation of the separate conveyor assemblies, saidframe spacing means including means for sensing when a predeterminedspacing exists between the frames to cause one of the conveyorassemblies to change its speed of operation so that the frames areprevented from bumping into each other.
 13. In a multiple layer coatingapparatus for coating substrates carried by frames disposed in generallyhorizontal positions, means forming at least one coating chamber, avertically disposed coating material source in the coating chamber forvaporizing at least one material for carrying out coating operations inthe coating chamber whereby the vaporized material moves upwardly, meansforming an entrance chamber, means forming an exit chamber, valve meansdisposed at opposite ends of each of the entrance and exit chambers,means for creating a vacuum condition in the coating chamber, separateconveyor assemblies provided in each of the entrance chamber, thecoating chamber and the exit chamber for receiving and advancing theframes and substrates therethrough so that the frames carrying thesubstrates and the substrates are maintained in a generally horizontalposition in at least the coating chamber with the bottom sides of thesubstrates being exposed to the vapor stream from the source, framespacing means for controlling the operation of the separate conveyorassemblies whereby a frame with a substrate thereon is advanced rapidlyout of the entrance chamber and toward the coating chamber and israpidly advanced into the exit chamber from the coating chamber, meansfor causing the conveyor assembly in the coating chamber to be operatedat a substantially constant speed which is slower than the speeds atwhich the conveyor assemblies in the entrance and exit chambers areoperated, means forming an additional chamber between said entrancechamber and said coating chamber and an additional conveyor assemblymounted in said additional chamber operable at a fast speed and at aslow speed with a fast speed corresponding to the speed of the conveyorassembly in the entrance chamber and with the slow speed correspondingto the speed of the conveyor assembly in the coating chamber, said framespacing means including means for sensing when a predetermined spacingexists between certain of the frames to cause the additional conveyorassembly to change from a fast speed of operation to a slow speed ofoperation, said means for sensing the spacing between the framesincluding a photocell assembly with a plurality of photocells arrangedlongitudinally of the direction of travel of the frames and means fordirecting collimated beams of light onto the photocells, said beams oflight being adapted to be interrupted by frames travelling through theframe spacing sensing means, and means for causing the additionalconveyor assembly to operate at the slow speed when the light beamsthrough more than a predetermined number of photocells are interruptedby the frames.
 14. In a multiple layer coating apparatus for coatingsubstrates carried by frames disposed in generally horizontal positions,means forming at least one coating chamber, a vertically disposedcoating material source in the coating chamber for vaporizing at leastone material for carrying out coating operations in the coating chamberwhereby the vaporized material moves upwardly, means forming an entrancechamber in communication with the coating chamber, means forming an exitchamber in communication with the coating chamber, valve means disposedat opposite ends at each of the entrance and exit chambers for sealingsaid exit and entrance chambers and interrupting communication with saidcoating chamber, means for creating a vacuum condition in the coatingchamber, a separate driven conveyor assembly provided in each of theentrance chambers, the coating chamber and the exit chamber forreceiving and advancing the frames and substrates therethrough so thatthe frames carrying the substrates and the substrates are maintained ingenerally horizontal positions in at least the coating chamber with thebottom sides of the substrates being exposed to the vapor stream fromthe source, said driven conveyor assembly in the coating chamber havinga horizontal supporting surface upon which said frames are adapted torest during travel through the coating chamber, said separate drivenconveyor and said coating chamber being driven at a substantially unformslow speed, said valve means being movable to open positions to permitsaid frames to pass therethrough, said driven conveyor assemblies insaid entrance chamber and said exit chamber being capable of beingdriven at a fast speed in comparison to said slow speed, frame sparingmeans including means for sensing the spacing between frames forcontrolling the operation of the conveyor assemblies whereby a frame ismoved rapidly out of the entrance chamber toward the coating chamberuntil a predetermined spacing exists between it and the preceding framefor maintaining a predetermined minimum spacing between the framesduring their travel through the coating chamber, seal duct means mountedbetween said entrance chamber, said coating chamber and said exitchamber so that a pressure differential can be maintained between saidchambers, said seal duct means including means for supplying heat to thesubstrate at the same time that the substrate is passing through theseal duct means, said seal duct means being formed of a sheet meterialhaving a relatively high resistance to form electrical heating means andmeans for supplying a current to said sheet material.